1. Field of the Invention
The invention relates in general to a semiconductor package structure, and more particularly to a semiconductor package structure formed by flip chip jointing technique.
2. Description of the Related Art
In the past few years, as the electronic products are developed toward being thin and small, multi-functioned, and high-speed, high-density and high input/output semiconductor package structures are required increasingly. For this reason, the flip chip package structure is now widely applied in the high-performance products and portable electronic products. In addition that the interface jointing paths can be reduced in the flip chip package technique to provide an excellent electrical feature, the whole package structure scale can be reduced meanwhile the multi-input/output pins requirement can be achieved by a suitable chip layout.
In the flip chip package structure, the surface of the chip, having solder bumps is directed to the substrate and the chip is jointed to the substrate directly via the bumps, different from the conventional wire bonding or tape automated bonding (TAB). The present flip chip jointing technique is mostly applied in the flip chip on board (FCOB), in which the chip is directly disposed on the substrate, or the flip chip in package (FCIP), which collocates the package structure CSP, BGA, or MCM, such as FC-CSP, FC-BGA, or FC-MCM.
Referring to FIG. 1, a lateral view of the conventional flip chip package structure is shown. Several solder bumps 104 are disposed on the first surface 102a, and form as bonding joints in the solder reflow process to electrically couple the semiconductor component 102 and the substrate 106. Solder balls 108 are disposed on the lower surface 106b of the substrate 106 for electrically coupling the flip chip package structure and the exterior circuits. The stress generated at the bonding joints for the flip chip expands when hot and shrinks when cold will damage the joints and reduce the reliability on the bonding of the semiconductor component 102 and the substrate 106. Therefore, an underfill process is generally used to fill underfill 110 in the region between the semiconductor component 102 and the substrate 106. By using the underfill 110 to tightly joint the semiconductor component 102 and the substrate 106, the stress at joints can be reduced as scattered to the underfill 110, and the ability of resisting the thermal fatigue at the joints can be improved.
In the conventional underfill process, the underfill 110 is filled in through one side or two sides of the semiconductor component 102, and distributed between the semiconductor component 102 and the substrate 106 by capillarity. Therefore, the upper surface of the substrate 106, contacting with the underfill, has to be larger than the lower surface of the semiconductor component 102 contacting with the underfill. That is, the area of the substrate 106 surrounded by the side surfaces 106p is larger than the area of the semiconductor component 102 surrounded by the side surface 102p, so the substrate 106 can provide enough space for the underfill flow. After the underfill 110 coats all the solder bumps 204 and fills in the region between the semiconductor component 102 and the substrate 106, and a part of the side surfaces 102p, the flip chip package structure 100 is put in an oven where the underfill is heated for solidification. However, in the process as the underfill is flowing or is being heated, the underfill will usually overflow and pollute the substrate 106. Especially when the size of the substrate is limited, such as the upper surface of the substrate is limited about equal to the lower surface of the semiconductor, in the process as the underfill is flowing or being heated, the substrate can not provide enough space for the underfill to flow. Therefore, the underfill will overflow to pollute the substrate, or even overflow to the solder balls on the lower surface of the substrate, thereby damaging the whole product.
Referring to FIG. 2, a lateral diagram of another conventional flip chip package structure is shown. The flip chip package structure 200 includes a semiconductor component 202, solder bumps 204, a substrate 206, solder balls 208, underfill 210 and dams 212. As shown in FIG. 2, several solder bumps 204 are disposed on the first surface 202a of the semiconductor component 202. The solder bumps 204 are jointed to the first surface 202a in the solder reflow process so that the first surface 202a of the semiconductor component 202 can be electrically coupled to the upper surface 206a of the substrate 206 via these solder bumps. The underfill 210 is used for coating the solder bumps 204 and tightly jointing the semiconductor component 202 and the substrate 206. The dam 212 projects from the upper surface 206a of the substrate 206. Due to the dam design, in the underfill process when the underfill 210 is filled in the region between the semiconductor component 202 and the substrate 206, and a part of the side surfaces 202p, the underfill overflow issue can be solved through the blocking of the dams 212.
However, in FIG. 2, in addition that the upper surface 206a of the substrate 206 has to be larger than the first surface 202a of the semiconductor component 202, the inner surface 212p of the dam 212 has to be outside the area on the substrate 206 projected by the first surface 202a of the semiconductor component 202, so that the substrate 206 can provide enough space for the underfill 210 flow. As a result, when a vertical view of the second surface 202b of the semiconductor 202 is taken, the underfill 210 and the dams 212 can be seen to surround the semiconductor component 202 layer by layer, which will influence the appearance of the flip chip package structure 200. Moreover, for the dams has to project from the substrate 206, which will increase the size of the substrate 206, such design cannot be applied to the flip chip package structure in which the lower surface of the semiconductor is almost equal to the upper surface of the substrate.